A survey of the health status of parents and grandparents of patients with homocystinuria due to cystathionine synthase deficiency has been completed. The results obtained indicate that mild homocyst(e)inemia is not an important contributory factor to atherosclerotic disease in the general population and provide no support for current hypothesis which postulate such an association. Preliminary work has been initiated upon a questionnaire survey aimed at obtaining standardized information sufficient to provide insight into many presently unanswered questions as to clinical features of homocystinuria due to cystahionine Beta-synthase deficiency and the effects of various therapies not in use for this condition.